Suburban 3/4 Ton 4WD V8-305 5.0L (1986)
Idle Speed: Adjustments
Idle Speed
California
NOTE: On engines equipped with an Idle Speed Control (ISC) motor, idle speed is controlled by an electrical signal from the Electronic Control
Module (ECM). Do not use the ISC plunger to adjust curb idle. The motor varies idle speed from a base (minimum authority) to a high (maximum
authority) idle speed. Do not adjust unless diagnosis indicates a malfunction. Check for proper base and high idle speed as follows.
CAUTION: DO NOT disconnect or connect ISC connector with ignition "ON" as damage to the ECM may occur.
1. Perform preliminary procedures:
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Check and adjust ignition timing.
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Disconnect and plug vacuum lines for evaporative purge and EGR valve.
2. Before starting engine, place transmission in "PARK" (automatic) or "NEUTRAL" (manual), set parking brake and block drive wheels.
3. Connect dwell meter to Mixture Control (M/C) solenoid dwell lead. This is a green connection breaking out of the main wiring harness leading to
carburetor.
NOTE: Remember to set dwell meter on the six cylinder scale, regardless of the engine being tested.
4. Turn A/C "OFF".
5. Start engine and run until stabilized and in "closed loop" mode (dwell meter needle starts to vary).
6. Turn ignition "OFF".
CAUTION: Do not unplug ISC connector with ignition "ON" as damage to motor will occur.
7. Unplug connector from ISC motor.
8. Fully retract ISC plunger by applying 12 volts to terminal "C" ad grounding lead to terminal "D" of the ISC motor connection.
CAUTION: DO NOT leave battery voltage applied to motor longer than necessary to retract ISC plunger. Prolonged contact will damage motor.
Also, NEVER connect voltage source across terminal "A" and "B" as damage to the internal throttle contact switch will result.
9. Start engine and run until dwell meter needle starts to vary, indicating "closed loop" operation.
10. Place automatic transmission in "DRIVE".
